main() {
  print(Num.num_static);
  print(Num(1, 2));

  var num = Num(1, 2);
}

class Num {
  //静态成员变量,只能通过类名.调用
  static var num_static;

  //实例变量
  var mum_01;
  var mum_02;

  //构造方法,默认给实例变量赋值
  Num(this.mum_01, this.mum_02);

  @override
  String toString() {
    return 'Num{mum_01: $mum_01, mum_02: $mum_02}';
  }
}
